Self-ligating orthodontic brackets including a metal ligation cover hingedly connected to a bracket base

ABSTRACT

Self ligating orthodontic brackets include a bracket base and a ligation cover which interacts with the base in order to provide ligation of at least one arch wire associated with the base. The ligation cover is hingedly attached to the bracket base by a hinge (e.g., a film hinge, an elastomeric material, a mechanical hinge, and the like). The ligation cover comprises a metal for improved strength and durability of the bracket during use. The bracket base advantageously comprises a plastic or ceramic material for ease of formation and for reducing expense.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/774,197, filed Feb. 6, 2004, in the names of Norbert Abels and ClausH. Backes and entitled SELF-LIGATING ORTHODONTIC BRACKETS INCLUDING ALIGATION COVER HINGEDLY CONNECTED TO A BRACKET BASE, which is acontinuation of U.S. application Ser. No. 09/952,584, filed Sep. 12,2001, now U.S. Pat. No. 6,695,612, in the names of Norbert Abels andClaus H. Backes and entitled SELF-LIGATING ORTHODONTIC BRACKETSINCLUDING A LIGATION COVER HINGEDLY CONNECTED TO A BRACKET BASE. Forpurposes of this disclosure, the foregoing application is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to orthodontic brackets, more particularlyto self-ligating orthodontic brackets that include a bracket base, atleast one slot or other feature for receiving an arch wire, and aligation cover.

2. The Relevant Technology

Orthodontics is a specialized field of dentistry that involves theapplication of mechanical forces to urge poorly positioned, or crooked,teeth into correct alignment and orientation. Orthodontic procedures canbe used for cosmetic enhancement of teeth, as well as medicallynecessary movement of teeth to correct underbites or overbites (“buckteeth”). Orthodontic treatment can improve the patient's occlusion, orenhanced spatial matching of corresponding teeth.

The most common form of orthodontic treatment involves the use oforthodontic brackets and wires, which together are commonly referred toas “braces”. Orthodontic brackets, more particularly the bracket bases,are small slotted bodies configured for direct attachment to the front(or “labial”) surfaces of the patient's anterior, cuspid, and bicuspidteeth or, alternatively, for attachment to bands which are, in turn,cemented or otherwise secured around the teeth. Once the brackets areaffixed to the patient's teeth, such as by means of glue or cement, acurved arch wire is inserted into the slot of each bracket. The archwire acts as a template or track to guide movement of the teeth intoproper alignment. End sections of the arch wire are typically capturedwithin tiny appliances known as “buccal tubes” affixed to the patient'smolars.

There are two distinct classes of orthodontic brackets: those thatrequire the use of ligatures to fasten the arch wire to the bracket, andthose that are self-ligating. Before the emergence of self-ligatingbrackets, small ligature wires or elastomeric bands were necessary tohold the arch wire in a securely seated position in the brackets.Ligatures or some other form of fastening means are essential to ensurethat the tensioned arch wire is properly positioned around the dentalarch, and to prevent the wire from being dislodged from the bracketslots during chewing of food, brushing of teeth, or application of otherforces. One type of commercially available ligature is a small,elastomeric O-ring, which is installed by stretching the O-ring aroundsmall wings known as “tie wings” that are connected to the bracket body.Metal ligatures may also be used to retain arch wires within the bracketslots.

In an effort to simplify the process of installing braces, variousself-ligating brackets have been developed. The term “self-ligatingbracket” refers to a class of orthodontic brackets that include somesort of ligation cover or clasp which encloses or otherwise retains thearch wire within the slot of the base. There are both “passive” and“active” self-ligating orthodontic brackets. The term “passive” bracketrefers to brackets that only loosely retain the arch wire therein, suchthat considerable movement between the arch wire and bracket base ispossible. The term “active” bracket refers to brackets in which theself-ligating arch wire cover exerts force onto the arch wire, resultingin more precise and controlled tooth movement.

The first self-ligating bracket, known as the Russell bracket, wasdeveloped by Dr. Jacob Stolzenberg in the early 1930s. This bracket,which uses a set screw to ligate the arch wire within a slot of athreaded base, was revolutionary but perhaps ahead of its time becausethe concept of self-ligating brackets fell more or less into obscurityuntil the early 1970s.

In 1971, Dr. Jim Wildman of Eugene, Oreg. developed the EDGELOK bracket,which has a round body with a rigid labial sliding cap. A specialopening tool is used to move the slide occlusally for arch wireinsertion. When the cap is closed over the arch wire with fingerpressure, the bracket slot is converted to a tube. The EDGELOK bracketwas the first “passive” self-ligating bracket. That is, the bracket,while retaining the arch wire therein, does not exert pressure onto thewire. Instead, the arch wire is free to slide relative to the bracket.The EDGELOK bracket is described in U.S. Pat. Nos. 3,748,740 and3,854,207 to Wildman. Other patents to Dr. Wildman include U.S. Pat.Nos. 5,094,614, 5,474,446 and 5,863,199. In 1998, Dr. Wildman introducedthe TWIN-LOCK bracket, which includes a flat, rectangular slide, housedbetween the tie wings of an edgewise twin bracket.

A similar bracket to the EDGELOK bracket, called the MOBIL-LOCK bracket,was developed by Dr. Franz Sander of Ulm, Germany, which requires aspecial tool to rotate the semicircular labial disk into the open orclosed position.

Between 1976 and 1980, Dr. Herbert Hanson of Hamilton, Ontario, Canadadeveloped the SPEED bracket, which features a curved spring clip thatwraps occluso-gingivally around a miniaturized bracket body. The clip ismoved occlusally using special tools to permit arch wire placement, thenseated gingivally using finger pressure. The clip constrains andinteracts with the arch wire to some degree such that the SPEED bracketwas the first “active” bracket system.

In 1986, Dr. Erwin Pletcher developed the ACTIVA bracket, which has aninflexible, curved arm that rotates occluso-gingivally around acylindrical bracket body (see U.S. Pat. Nos. 4,077,126, 4,371,337,4,419,078, 4,522,490, 4,559,012 and 5,322,435 to Pletcher). The arm canbe opened and closed using finger pressure.

In 1995, Dr. Wolfgang Heiser of Innsbruck, Austria developed the TIMEbracket, which is similar in appearance to the SPEED bracket, and whichfeatures a rigid, curved arm that wraps occluso-gingivally around thelabial aspect of the bracket body. A special instrument is used to pivotthe arm either gingivally into the slot-open position, or occlusallyinto the slot-closed position. The stiffness of the bracket arm preventsany substantial interaction with the arch wire, thereby making the TIMEbracket a passive bracket.

Dr. Dwight Damon of Spokane, Wash. developed the Damon SL I and theDamon SL II brackets in 1996 and 1999, respectively (see U.S. Pat. No.6,071,118 to Damon). Both are edgewise twin brackets. The differencebetween the two is that the first features a labial cover that straddledthe tie wings, while the second incorporates a flat, rectangular slidebetween the tie wings. In both versions, the slide moves incisally onthe maxillary brackets and gingivally on the mandibular brackets.Special opening and closing pliers are required to move the slide.

There are many other variations and adaptations of the foregoingself-ligating brackets that have been developed by others. See, e.g.,U.S. Pat. No. 4,786,252 to Fujita, U.S. Pat. No. 4,712,999 to Rosenberg,U.S. Pat. No. 4,492,573 to Hanson, U.S. Pat. No. 4,103,423 to Kessel,and U.S. Pat. No. 6,071,119 to Christoff et al.

In general, conventional self-ligating brackets are complicated indesign, complex to assemble, and difficult to use in practice.Conventional orthodontic brackets often require many trips to theorthodontist for periodic readjustment and maintenance. Therefore, therehas been a long-felt need to find new designs and materials that cansimplify the manufacture of orthodontic brackets, as well as theinstallation and subsequent maintenance of such brackets. In particular,there is a need for orthodontic brackets that are easy to open andclose, that provide active ligation without the need for special toolsto open and close the arch wire restraining means, which are easilymanufactured and installed by the orthodontist, which provide greaterversatility together, and which are of simplified design.

For example, it would be an improvement in the art to provide one-piece,self-ligating orthodontic brackets that can be manufactured in a singlemolding step. It would be a further improvement to provide self-ligatingbrackets that include a plurality of plastic materials from which thebase and cover can be made so as to maximize the beneficial propertiesof each plastic material. It would be an additional improvement toprovide orthodontic brackets with special hinge and locking featuresbetween the ligation cover and bracket base or increased safety and easeof use. It would be an improvement to provide orthodontic bracketscapable of dynamic active ligation of an arch wire as the tooth isrealigned so as to reduce or eliminate the need for subsequentadjustments. It would yet be an improvement to provide orthodonticbrackets having two or more initially open arch wire slots that can beligated by a single ligation cover. It would also be an improvement toprovide a ligation cover that was biased so as to preferentially remainin an open and/or closed position.

Orthodontic brackets that incorporate one or more of these and otherimprovements are disclosed and claimed herein.

SUMMARY OF THE INVENTION

The orthodontic brackets according to the present invention encompassone or more of the improvements and features disclosed herein, whichresult in a generally low-cost bracket that is simple to manufacture,compact in construction, and easy to install and adjust.

In general, the orthodontic brackets according to the invention willinclude at least one of the following improved features:

-   -   1. a ligation cover that includes a film hinge, which is a        localized area of reduced cross-sectional thickness, about which        at least a portion of the ligation cover can rotate so as to        open and close relative to the bracket base;    -   2. a spring element extending from an underside of the ligation        cover and that is able to absorb mechanical energy from an arch        wire and then release such energy over time to provide        continuous active ligation of the arch wire;    -   3. a general spring feature associated with, or incorporated        into, the ligation cover that is able to absorb mechanical        energy from the arch wire and then release such energy over time        in order to provide dynamic active ligation of an arch wire        associated with a bracket base;    -   4. an orthodontic bracket that includes a deformable or flexible        ligation cover that facilitates locking and unlocking of the        cover relative to a bracket base that includes a lip, overhang        or other structure within which the ligation cover can be        slideably inserted or withdrawn;    -   5. a spring element interconnecting the ligation cover and        bracket base that urges the ligation cover to remain open while        in an open position and/or to remain closed while in a closed        position relative to the bracket base;    -   6. a ligation cover that is biased toward remaining open when in        an open position and toward remaining closed while in a closed        position, such that positive pressure or force is required to        selectively open and close the cover each time, and such that        the cover is optionally able to apply a ligation force onto an        arch wire associated with the bracket even when the ligation        cover is not securely locked to the bracket base;    -   7. an orthodontic bracket that is manufactured using two-color        molding of different types of plastic materials, such as a        harder, more durable plastic for the bracket base and a more        flexible and resilient plastic for the ligation cover;    -   8. an orthodontic bracket that includes at least two initially        open arch wire slots configured to accept or receive two or more        separate arch wires that can be at least partially occluded by a        single ligation cover in a single action of locking or closing        the ligation cover relative to the bracket base so as to ligate        the arch wires; or    -   9. an orthodontic bracket having a safety locking feature that        provides enhanced locking of the ligation cover to the bracket        in response to increased pressure by an arch wire bearing        upwardly against a ligation cover.

In general, depending on which of the foregoing features areincorporated into a particular orthodontic bracket, the orthodonticbracket may provide either passive or active ligation of an arch wireassociated with the bracket base. The bracket may include a bracket baseand ligation cover may be molded as a single, unitary piece, or elseformed separately and then joined together. The ligation cover may ormay not include specific hinge structures or regions, but may insteadbend or flex along a substantial length of the ligation cover. Anorthodontic bracket may be manufactured from a single plastic or metalmaterial, or from multiple materials, such as metal and plastic or twoor more plastics. The ligation cover may be flexible or rigid. Thebracket base may include a single arch wire slot or it may includemultiple arch wire slots. In some cases, the ligation cover will bedesigned to cover a single arch wire slot and in others, it may ligatetwo or more open slots. In some cases, one or more slots may be providedthat are not ligated by the ligation cover such that conventionalligatures may be required to ligate additional arch wires disposedtherein. Unless otherwise specified or restricted, any feature known inthe art of orthodontic brackets, bases and ligation covers may be usedin conjunction with a particular orthodontic bracket that encompasses atleast one of the improved features summarized above and disclosed morefully hereinafter.

These and other advantages and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto specific embodiments thereof which are illustrated in the appendeddrawings. Understanding that these drawings depict only exemplaryembodiments of the invention and are not therefore to be considered tobe limiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings, in which:

FIG. 1A is a cross-section view of a hinged, one-piece orthodonticbracket that includes a bracket base, a ligation cover, and a springelement interconnecting the ligation cover and bracket base, with thecover being “open” relative to the arch wire slot of the base;

FIG. 1B shows the orthodontic bracket of FIG. 1A with the ligation coverbeing “closed” or “locked” relative to the arch wire slot;

FIG. 2 is a cross-section view of a two-piece orthodontic bracket inwhich the ligation cover is separate from the bracket base;

FIGS. 3A and 3B depict a variation of the orthodontic bracket of FIG. 2in which the ligation cover is loosely connected to the bracket base bya leash;

FIG. 4A is a perspective view of a hinged orthodontic bracket thatincludes a ligation cover configured so as to substantially encase orsurround the bracket base when in a closed or locked position;

FIG. 4B shows the orthodontic bracket of FIG. 4A with the ligation coverbeing “closed” or “locked” relative to the arch wire slot;

FIG. 5A is a perspective view of a hinged, one-piece orthodontic bracketthat includes a leaf spring extending from an under side of the ligationcover and configured to engage an arch wire associated with the bracketbase;

FIGS. 5B and 5C are cross-section views of the orthodontic bracket ofFIG. 5A showing the kinematics of a spring element interconnecting theligation cover and bracket base;

FIGS. 6A and 6B are cross-section, close-up views of different lockingnotches for locking a ligation cover to a bracket base;

FIGS. 7A–7C is a cross-section view of a hinged orthodontic bracket thatincludes a ligation cover, a bracket base, a spring elementinterconnecting the cover and base, a bearing spring for engaging anarch wire, and channels or under cuts for enhanced adhesion to a tooth;

FIG. 8 depicts a variation of the orthodontic bracket of FIGS. 7A–7C,except that the ligation cover is separate and detachable from thebracket base;

FIG. 9A is close-up view of a serpentine bearing spring extendingpartially into an arch wire slot;

FIG. 9B is close-up view of a zig-zag bearing spring extending partiallyinto an arch wire slot;

FIG. 9C is close-up view of a coiled bearing spring extending partiallyinto an arch wire slot;

FIG. 9D is close-up view of a dual leaf spring extending partially intoan arch wire slot;

FIG. 10A depicts the orthodontic bracket of FIGS. 7A–7C being opened bya person's fingernail;

FIG. 10B depicts the orthodontic bracket of FIGS. 7A–7C being opened bya common dental tool;

FIGS. 11A–11B depict different numbers of trapezoidal under cuts used inpromoting better adhesion between an orthodontic bracket and a tooth;

FIGS. 12A–12B depict an orthodontic bracket having a serpentine bearingspring in varying stages of compression due to the orientation of thearch wire relative to the bracket base;

FIG. 13A is a perspective view of an orthodontic bracket that includes aspecial locking feature that locks the ligation cover more tightly tothe bracket base in response to increased upward pressure from an archwire to the ligation cover;

FIG. 13B is a perspective view of the orthodontic bracket of FIG. 13Awith the ligation cover in a locked position.

FIG. 13C is a perspective view of the underside of the orthodonticbracket of FIG. 13A.

FIGS. 14A and 14B are side views of the orthodontic bracket as depictedin FIGS. 13A and 13B, respectively.

FIGS. 15A and 15B are cross-section views of the orthodontic bracket ofFIGS. 13 and 14 showing how a ligation cover arching upwards in responseto pressure by an arch wire causes a locking tongue of the ligationcover to be withdrawn more tightly into an angled key way of the bracketbase;

FIG. 16A is a cross-section view of a two-piece orthodontic bracket thatincludes special locking features on both sides, with the ligation coverremoved;

FIG. 16B is a cross-section view of the orthodontic bracket of FIG. 16Awith the ligation cover attached;

FIGS. 17A and 17B show an alternative embodiment of a hinged, one-pieceorthodontic bracket having the special locking feature of theorthodontic bracket of FIGS. 13–15;

FIGS. 18A and 18B show an alternative embodiment of a hinged, two-pieceorthodontic bracket having the special locking feature of theorthodontic bracket of FIGS. 13–15;

FIG. 18C shows an alternative embodiment of a hinged, two-pieceorthodontic bracket having the special locking feature of theorthodontic bracket of FIGS. 13–15 and a separate hinge materialinterconnecting the ligation cover and bracket base;

FIGS. 19A and 19B depict an orthodontic bracket having an angled archwire slot;

FIGS. 20A and 20B depict a hinged, two-piece orthodontic bracket havinga spring element and special locking feature similar to the bracket ofFIGS. 13–15;

FIG. 21A is a perspective view of an orthodontic bracket in which theligation cover and bracket base are formed from different types ofplastic materials that are fused or otherwise bonded together to form anintegral orthodontic bracket of essentially one piece;

FIG. 21B is a cross-section view of the orthodontic bracket of FIG. 21Aof showing how the ligation cover hingedly rotates about an integralhinge element interconnecting the ligation cover and bracket base;

FIG. 21C is a cross-section view of the orthodontic bracket of FIGS. 21Aand 21B showing how the ligation cover is able to absorb mechanicalenergy from an arch wire bearing upwardly against the cover;

FIG. 22 is a perspective view of an orthodontic bracket that is similarto the bracket depicted in FIGS. 21A–21C, except that the ligation coveris shorter and extends over only a portion of the bracket base;

FIGS. 23A–23C depict an orthodontic bracket having a flexible ligationcover that is able to be locked and unlocked relative to the bracketbase primarily due to the flexibility of the cover and its ability to beslidably inserted into and withdrawn from a lip or overhang in thebracket base;

FIGS. 24A and 24B show a two-piece orthodontic bracket in which theligation cover and bracket base have been separately formed andmechanically joined and affixed together;

FIGS. 25A and 25B depict a two-piece orthodontic bracket in which theligation cover is hingedly attached to the bracket base by means of amechanical hinge and which is capable of enclosing two initially openarch wire slots;

FIG. 25C is a cross-section view of a two-piece orthodontic bracket inwhich the ligation cover is completely detachable from the bracket baseand which is capable of enclosing three initially open arch wire slots;and

FIGS. 26A and 26B show a two-piece orthodontic bracket having a filmhinge in a location other than where the ligation cover is attached tothe bracket base.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction and Definitions.

The present invention encompasses a number of separate but interrelatedinventive concepts and embodiments that greatly improve the ease,simplicity and efficiency with which a dental practitioner can attachand adjust orthodontic appliances known as orthodontic brackets,commonly referred to as “braces”. They also increase the effectivenessof treatment and reduce discomfort by the patient. In many cases, theinventive orthodontic brackets are less expensive to manufacture, sincethey are amenable to being injection molded from plastic in a singlestep.

By greatly reducing the time, cost and effort in manufacturing andinstalling orthodontic brackets, the present invention makes it possiblefor orthodontic brackets and procedures to be more widely available tothe less affluent. Their increased comfort compared to conventionalbrackets also makes them more attractive to all users of orthodonticbrackets.

The orthodontic brackets according to the invention include a bracketbase and a ligation cover or clasp. The ligation cover can beselectively opened in order to permit the insertion of an arch wire intoan arch wire slot or other feature within the base and then closed orlocked in order to retain the arch wire within the slot or otherfeature.

The orthodontic brackets according to the invention include both passiveand active ligating brackets (i.e. those in which the ligation coverexerts pressure onto the arch wire and covers that do not), brackets inwhich the bracket base and ligation cover are manufactured as oneunitary piece and those in which the base and cover are formedseparately and then joined together, covers that have specificallyformed hinge structures or regions (e.g., film hinges or pivot pins) andthose with no specific hinge structure or region, brackets made of asingle material (e.g., plastic or metal) and those comprising multiplematerials (e.g., plastic and metal and/or two or more differentplastics), covers that are flexible and those that are rigid, bases thatinclude a single arch wire slot and those that include two or moreslots, bases in which ligation of the arch wire is only possible byclosing or locking the ligation cover and those that also includestructures that permit optional ligation using conventional ligatures.

The orthodontic brackets may optionally include one or more specialfeatures, such as leaf springs and the like, that extend from the covertoward the arch wire slot in order to provide dynamic active ligation asthe arch wire is more fully seated within the arch wire slot over time.They may alternatively include a more rigid protrusion extending from aflexible ligation cover that is able to absorb mechanical energy fromthe arch wire and then transfer such energy over time to the tooth inorder to provide dynamic active ligation in a different manner. Thebrackets may optionally include a special safety locking feature betweenthe base and cover that results in a tightening of the cover to the basein response to increasing upward pressure from the arch wire to thecover. The brackets may optionally include a spring feature that urges aclosed cover to remain closed and/or an open cover to remain open, suchthat positive force is required to move the cover from an open positionto a closed position and/or from a closed position to an open position.

The terms “orthodontic bracket” and “bracket”, for purposes of thisdisclosure and the appended claims, and unless otherwise specified orlimited, shall be broadly understood as referring to an orthodonticappliance that can be attached to, and used to straighten, a tooth.Unless otherwise specified or limited, such “orthodontic brackets” will,at a minimum, include a bracket base and a ligation cover. Unlessotherwise specified or limited, the terms “orthodontic bracket” and“bracket” shall not be understood as implying the use of any particulartype of material, the inclusion of any particular design feature, theability to provide any particular function, or any constraint as to itsmode of use.

The terms “bracket base” and “base”, for purposes of this disclosure andthe appended claims, and unless otherwise specified or limited, shall beunderstood as referring to that portion of an orthodontic bracket thatis attached to a tooth and that includes at least one slot or otherstructural feature for receiving or holding an arch wire therein. Theterm “bracket base” shall be understood as encompassing any of theexemplary bases disclosed herein, as well as any bracket bases known inthe art of orthodontics, unless otherwise specified or limited. Unlessotherwise specified or limited, the term “base” shall not be understoodas implying the use of any particular type of material, the inclusion ofany particular design feature, the ability to provide any particularfunction, or any constraint as to its mode of use.

The term “arch wire slot”, for purposes of this disclosure and theappended claims, and unless otherwise specified or limited, shall beunderstood as referring to any depression, groove, enclosure, region, orspace adjacent one or more protrusions or raised portions within thebase of an orthodontic bracket that is designed so as to at leastpartially receive an arch wire therein or thereat. The “arch wire slots”according to the invention are not limited to any particular size, shapeor arrangement. The term “arch wire slot” shall be understood asencompassing any of the exemplary arch wire slots disclosed herein, aswell as any arch wire slots known in the art of orthodontics, unlessotherwise specified or limited.

The term “arch wire”, for purposes of this disclosure and the appendedclaims, and unless otherwise specified or limited, shall be understoodas referring to any initially straight or curved wire or elongatedstructure that is used to interconnect at least one orthodontic bracketwith another orthodontic bracket or structure for the purpose ofrealigning one or more misaligned teeth. The term “arch wire” shall beunderstood as encompassing any of the exemplary arch wires disclosedherein, as well as any arch wires known in the art of orthodontics,unless otherwise specified or limited. Unless otherwise specified orlimited, the term “arch wire” shall not be understood as implying theuse of any particular type of material, the inclusion of any particulardesign feature such as size or cross-sectional shape, or the ability toprovide any particular function other than the application ofstraitening forces onto one or more misaligned teeth.

The term “ligation cover”, for purposes of this disclosure and theappended claims, and unless otherwise specified or limited, shall beunderstood as referring to that portion of an orthodontic bracket thatis used to hold, lock, affix or otherwise retain an arch wire within atleast a portion of the slot, structural feature or region within thebase for receiving or holding arch wires, e.g., by at least partiallyoccluding one or more arch wire slots. Unless otherwise specified orlimited, such “ligation covers” may be designed so as to cover all orany portion of the arch wire slot, and all or any portion of the base,so long as ligation of the arch wire occurs while the ligation cover isin a closed or locked position relative to the base. The term “ligationcover” shall be understood as encompassing any of the exemplary ligationcovers disclosed herein, as well as any ligation cover known in the artof orthodontics, unless otherwise specified or limited. Unless otherwisespecified or limited, the term “ligation cover” shall not be understoodas implying the use of any particular type of material, the inclusion ofany particular design feature, the ability to provide any particularfunction other than to selectively ligate and release at least one archwire, or any constraint as to the manner in which it is attached to thebase.

The term “hinge”, for purposes of this disclosure and the appendedclaims, and unless otherwise specified or limited, shall be understoodas referring to any of one or more structural features or regions withina ligation cover, or between a ligation cover and base, that permits theligation cover to pivot or rotate relative to the bracket base to whichit is attached. Thus, a “hinge” may define a region where one end of aligation cover is hingedly attached to a bracket base, and/or a centerpoint or line about which the ligation cover may rotate. Hinges may alsointerconnect a spring with a ligation cover and/or a bracket base. Theterm “hinge” shall be understood as encompassing any of the exemplaryhinges disclosed herein, as well as any hinge known in the orthodonticor general mechanical arts, unless otherwise: specified or limited.Unless otherwise specified or limited, the term “hinge” shall not beunderstood as implying the use of any particular type of material, theinclusion of any particular design feature, or the ability to provideany particular functions other than those commonly provided by hinges ingeneral.

As clearly shown in the drawings and inherent in the disclosure, a hingemay be designed that permits the ligation cover to rotate about thehinge over a substantial angle of rotation between an open, non-ligatingposition and a closed, ligating position relative to the bracket base(e.g., to an open, non-ligating position in which no portion of theligation cover remains directly above the arch wire slot). The ligationcover may rotate freely or less freely about the hinge depending on thetype of hinge and/or whether the bracket includes a spring.

The term “latch for locking the ligation cover to the base” (or forbrevity, “latch member” or “cover locking clasp”), for purposes of thisdisclosure and the appended claims, and unless otherwise specified orlimited, shall be understood as comprising any locking device,mechanism, slot, recess, flange or protrusion, or any set ofinterlocking, overlapping or interacting mechanical features that serveto secure an initially free, rotatable or flexible end of a ligationcover to the bracket base, such as to achieve ligation of an arch wirelocated at least partially within an arch wire slot. Such “latchmembers” or “cover locking clasps” may advantageously permit selectivelocking and unlocking of the ligation cover to the base, althoughpermanent or irreversibly locking “latches” or “clasps” may be usedwithin the scope of the invention. Even though the terms “latch” or“clasp” may, in some cases, refer to specific mechanical features thatare integrally part of the ligation cover and base, they are not solimited and may include additional mechanical structures or featuresthat are separate from the ligation cover and base. Thus, the terms“latches” or “clasps” shall be understood as encompassing any of theexemplary locking clasps or latches disclosed herein, as well as anylocking latch or clasp known in the orthodontic or general mechanicalarts, unless otherwise specified or limited. Unless otherwise specifiedor limited, the terms “latch” and “clasp” shall not be understood asimplying the use of any particular type of material, the inclusion ofany particular design feature, or the ability to provide any particularfunctions other than those commonly provided by locking clasps ingeneral.

The term “spring”, for purposes of this disclosure and the appendedclaims, and unless otherwise specified or limited, shall be understoodas comprising any device or material that generally tends to assume aparticular conformation when relaxed, and which requires the applicationof an external force in order for the spring to assume a differentconformation, such as being compressed or elongated. The term “spring”includes any device or material that, when compressed, elongated orotherwise manipulated by a force so that it is no longer in a relaxedconformation, continuously exerts an opposing force until it reassumesthe relaxed conformation such that it is capable of storing mechanicalenergy. Hence, unless otherwise specified or limited, the term “spring”shall be broadly understood as encompassing any “energy storing springs”disclosed herein and also any such springs known in the orthodontic andgeneral mechanical arts.

Nevertheless, the term “spring” may, in some cases where specified, alsoinclude those devices and materials that are said to have “elasticmemory” such that they can become at least partially “relaxed” whenforced to assume a particular conformation over a time sufficient forany initially opposing forces to at least partially subside. In otherwords, there are polymers and other materials that, when assuming anoriginal relaxed conformation, initially resist and exert a forceopposite to a conformation-changing force but which, over time, canbecome substantially relaxed in a new conformation such that they mayactually resist a conformation-changing force that seeks to return thematerial to the original conformation. Hence, the term “spring” may, insome cases, also refer to materials that possess such “elastic memory”.

For the sake of simplicity, directional terms such as “top”, “bottom”,“up”, “down”, “upper”, “lower”, and “under side”, for purposes of thisdisclosure and the appended claims, shall be understood in reference toa tooth surface upon which, an orthodontic bracket is attached or isintended to be attached, with the tooth surface lying “beneath” thebracket, and the bracket sitting “above” the tooth surface. Thus, unlessotherwise specified, it shall be assumed that any direction moving awayfrom the tooth surface is “up” and any direction moving toward the toothsurface is “down”. In general, the ligation cover extends over at leasta portion of an “upper” surface or region of the bracket base when in alocked position. The surface or region of the bracket base that mostclosely approaches or is adjacent the tooth surface is the “bottom” or“under side” of the base. The region or side of the ligation cover thatis adjacent to the bracket base while in a locked position is the “underside” of the cover.

II. Orthodontic Brackets.

The orthodontic brackets according to the invention generally include abracket base and a ligation cover. The base is the portion of theorthodontic bracket that is attached or adhered to a tooth. Theexemplary bases depicted in the drawings and described more fully belowinclude one or more arch wire slots that are able to receive orgenerally hold or retain an arch wire in an initially unligated fashion.The ligation cover is the mechanism or means by which an arch wire isligated or held in place within the arch wire slot. Alignment forcesexerted by one or more arch wires to the base and/or cover aretransferred to the tooth in order to urge the tooth into properalignment. The present invention contemplates the use of a wide varietyof different bracket bases and ligation covers having varying mechanicaland functional features. The following discussing is intended to merelyexemplify specific embodiments or species of the larger genus of bracketbases and ligation covers that can be used in making the orthodonticbrackets according to the invention. It should be understood thatvirtually any base and ligation cover known in the art, in view of theteachings disclosed herein, can be used or modified so as to function ina manner contemplated by the present invention.

A. Materials.

The bracket bases and ligation covers according to the invention can bemade from any suitable material, or groups of materials, having desiredproperties, such as strength, rigidity, durability, flexibility,resilience, moldability, or machinability. Two suitable classes ofmaterials that are widely used in making bases and ligation coversinclude metals and plastics. Ceramics or other rigid materials mayalternatively be used in manufacturing bases for use in the invention.In the case of plastics or ceramics, strengthening fibers may be addedto increase the strength, toughness and resiliency of the finished baseand/or ligation cover.

A suitable metal that may be used to manufacture bases and ligationcovers includes, for example, stainless steel. The metals selected foruse in making the base should be safe when employed in the oral cavity.In other words, metals that are dangerous when ingested should generallybe avoided unless they are somehow encapsulated or otherwise preventedfrom diffuising in significant quantity into the person's saliva.

Suitable plastics for making bases and ligation covers include, but arenot limited to, polyoxymethylene, PEEK, polycarbonates, PET, otherpolyesters, polyamides, polyaramides, and the like. For the sake ofbrevity, the term “plastic” shall broadly include thermoplastic andthermoset materials. The term “plastic” may be used to describevirtually any organic polymer or copolymer having suitable properties ofmoldability and hardenability. In general, harder plastics are generallypreferred in order to provide a rigid, stable bracket base. Of course,virtually any plastic that can safely be employed in a person's mouth,and that has sufficient strength, toughness and rigidity for use as abase, is within the scope of the invention. Whereas softer, moreflexible plastics such as polyethylene and polypropylene are generallyless suitable for use in making the bracket base, since it is typicallydesirable for the base to have high hardness and durability, they may beadvantageously employed in the manufacture of ligation covers,particularly where it is desired for a ligation cover to be moreflexible than the bracket base.

As will be discussed more fully below, the bracket base and ligationcover can be made from the same material. In some cases it may be morecost effective from the standpoint of manufacturing costs, as well asproviding greater ease of use, to mold the base and cover as a singlepiece. In the case where a more rigid plastic is used in making thebase, and a more flexible plastic is used in making the cover, it willtypically be advantageous to separately mold the bracket base andligation cover and then thermally fuse them together to form a single,integrally connected bracket. This procedure is sometimes referred to inthe art of molding as “two-color molding”, which refers to the fact thattwo different plastic materials are molded or fused together to form asingle integral, or one-piece, article of manufacture.

As will be discussed more fully below, the ligation cover and base maybe joined together using bridging fibers or a fabric to form a flexiblejoint. In such a case, the fibers or fabric may advantageously bepartially embedded within the material used to form the base andligation cover (e.g., plastic) while in a plastic or molten state.

It is within the scope of the invention to employ a combination of twoor more materials when making an orthodontic bracket, such as a metalbase and plastic ligation cover or, alternatively, a plastic base andmetal ligation cover. Two or more materials such as plastic and metalmay be used in making the base, or in making the ligation cover, witheach material performing a function that is unique and specific to thatmaterial. Separately formed metal materials may be joined together, forexample, by means of one or more mechanical fasteners (e.g., hinges,rivets, pins, screws, interlocking pieces, etc.), welds, adhesives orcements. As more fully discussed below, a plastic base may be reinforcedwith metal attachments or inserts to provide greater durability and wearlife, particularly where a metal implement (e.g., an arch wire) makesforceful contact with the base. The ligation cover may likewiseincorporate a metal feature that comes into direct contact with the archwire to provide greater durability. A material that more readily acceptsadhesives may be used on the bottom of the base next to the tooth.

B. Exemplary Orthodontic Brackets.

FIGS. 1–26 depict exemplary orthodontic brackets that incorporate one ormore of the inventive concepts disclosed herein. Based on the specificdescriptions of the exemplary brackets, together with the generalprinciples set forth herein, one of ordinary skill in the art will bereadily able to modify any of the exemplary brackets to include anyother features described or suggested herein, either generally or in thecontext of a different embodiment. Moreover, one of ordinary skill willreadily appreciate that existing orthodontic brackets may also bereadily modified, in light of the advantages that will become apparentwhen reading the present description, so as to incorporate one or moreof the inventive concepts or features disclosed herein.

A first exemplary orthodontic bracket is shown in FIGS. 1A–1B.Orthodontic bracket 10 includes a generally anvil-shaped bracket base 12and a ligation cover 14 connected thereto. The bracket base 12 includesan arch wire slot 16 for receiving an arch wire 18 therein. Althoughshown as having a square cross section, the arch wire 18 can have anydesired cross section, such as rectangular, circular, oval, andcombinations thereof (e.g., part angular and part curved). The arch wireslot 16 can have any desired configuration. Because arch wires aretypically made of metal, and in the case where the bracket base 12 ismade of plastic, as depicted in FIGS. 1A and 1B, it may be advantageousto include a reinforcement insert 20 that is made of metal, ceramic, ora more durable plastic in order for the bracket base to have greaterdurability and resistance to wear where it comes into contact with anarch wire. In an exemplary molding process, the plastic base 12 may bemolded around a metallic or ceramic reinforcement insert, such as insert20. Bracket base 12 further includes auxiliary recesses 38 on eitherside, which can be used to optionally secure the arch wire 18 within theslot 16 using conventional wire or elastomeric ligatures, such as wherethe ligation cover 14 has been permanently removed or separated from thebracket base 12 (e.g., by severing or tearing). Thus, when the ligationcover 14 is removed, the base 12 may at least approximately resemble aconventional bracket.

The ligation cover 14 is shown as being generally L-shaped so as tohingedly connect to the bracket base 12 at one end of the “L” (by hingeelement 22 discussed below), and overlap and lock around the base 12 atthe other end. A plurality of locking notches 32 within a latch member31 assist in locking the ligation cover 14 over a protrusion 34 withinthe bracket base 12. The notches 32 provide a plurality of lockingpositions, or degrees of closure, of the ligation cover 14 in order toprovide the orthodontic practitioner with the ability to apply varyinglevels of force onto the arch wire 18. A bearing or holding cam 36extends downwardly from the ligation cover 14 and partially into thearch wire slot 16 when the cover 14 is in a closed or locked position(FIG. 1B) in order to apply direct pressure to the arch wire 18 andthereby provide active ligation.

In the case where the plastic ligation cover 14 depicted in FIGS. 1A and1B has sufficient flexibility and resiliency, the ligation cover 14 willbe able to flex upwardly and thereby absorb mechanical energy within anarch wire 18 that is not entirely seated within the arch wire slot 16,such as where the tooth (not shown) to which the orthodontic bracket 10is attached is misaligned in a lingual direction. In this manner, theligation cover 14 is able to provide continuous active ligation even asan arch wire that is initially not seated within the slot 16 becomesseated as the base 12 moves outward during realignment of the tooth.Moreover, the arch wire energy absorbed by the ligation cover 18 iscontinuously released and transferred through the base 12 to the toothas the tooth moves into proper alignment. Thus, the flexation andsubsequent release of mechanical energy by the ligation cover 18,coupled with continuous active ligation of the arch wire 18 by thebracket 10, advantageously results in dynamic active ligation of thearch wire over a wide range of tooth positions during realignment of thetooth. This, in turn, eliminates the need for, or at least reduces thefrequency of, adjustments to the orthodontic bracket 10 over the courseof tooth realignment.

The orthodontic bracket 10 as shown in FIGS. 1A and 1B includes a hingeelement 22 that integrally connects the ligation cover 14 to the bracketbase 12 and comprises the same material. In this way, the ligation cover14 and bracket base 12 can be molded, such as by injection molding, in asingle molding step to yield an integral, one-piece orthodontic bracket10. In a preferred embodiment, the integral hinge 22 comprises an areaor region of locally reduced cross-sectional thickness in order toprovide increased flexibility in the hinge region. Such a hinge may bereferred to as a “film hinge”. In this way, the film hinge 22 provides acenter point or line of rotation about which the ligation cover 14 canbe rotated back and forth between an open position, in which the archwire slot 16 is completely open (FIG. 1A), and a closed or lockedposition, in which the arch wire slot 16 is completely enclosed in orderto provide ligation of an arch wire disposed therein (FIG. 1B).

Interconnecting the ligation cover 14 and the base 12 is a springelement 24. The spring element 24 is also depicted as comprising thesame material as ligation cover 14 and bracket base 12 such that theentire bracket 10 can be molded as a single piece. The spring element 24is connected to the base by hinge element 26 and to the ligation cover14 by hinge element 28. Hinge elements 26 and 28 are also depicted ascomprising film hinges of reduced cross-sectional thickness.Nevertheless, as will be shown in later embodiments, the spring element24 may be attached to the cover 14 and base 12 using any desired hingeor other connection means known in the art. In order for the spring 24to lay substantially flush with the ligation cover 14 when the cover isin a closed and locked position, the cover 14 may include a region 30 ofreduced cross section into which the spring 24 can insert itself duringclosure of the ligation cover 14. In this way, the ligation cover 14 andspring 24 yield a smooth, continuous and uniform upper surface whenclosed. This, in turn, reduces the tendency of food, plaque or otherdebris to become lodged in the orthodontic bracket 10 while in use. Italso yields a bracket having a minimum of uncomfortable jagged edgescompared to conventional brackets.

Spring element 24 acts to urge the ligation cover 14 to remain openwhile in the open position depicted in FIG. 1A, and to remain closedwhile in the closed position depicted in FIG. 1B. The dynamics of howspring element 24 accomplishes this is more particularly illustrated inFIG. 1A. As shown therein, the point where the spring 24 interconnectswith the ligation cover 14 (i.e. at hinge element 28) moves along acircular arc A₁, which is defined by a radius R₁ having its origin athinge element 22, as the cover 14 is selectively moved between an openand closed position. On the other hand, were it not for the connectionat hinge element 28 between the spring element 24 and the ligation cover14, a hypothetical free end of spring element 24 would instead movealong theoretical arc A₂, which is defined by a radius R₂ having itsorigin at hinge element 26 interconnecting the spring 24 and the bracketbase 12. Thus, due to the connection between spring 24 and cover 14 athinge 28, the end of the spring 24 distal to hinge 26 is forced totravel beyond arc A₂ and along arc A₁, thereby elastically deforming thespring 24 as the cover 14 is moved between the open and closed position.

The maximum extension of spring element 24 is shown as distance X, whichis the maximum distance between arcs A₁ and A₂. Hence, force is requiredto move the cover 14 in either direction toward the location of distanceX. Conversely, the spring will contract and thereby urge the cover 14away in either direction from the location of distance X. Accordingly,whether the spring 24 will urge the cover 14 either into an openposition or a closed position depends on where hinge 28 is locatedrelative to the location of distance X. Although distance X is depictedas being located approximately midway between the open and closedpositions of ligation cover 14, one of ordinary skill in the art willappreciate that the orthodontic bracket can be designed so as toposition distance X at any desired location depending on how one wishesthe spring 24 to behave.

FIG. 2 depicts an orthodontic bracket 10′ that is similar to the onedepicted in FIGS. 1A and 1B, except that it is a two-piece bracket,i.e., the ligation cover 14′ is not integrally connected to the base 12.The ligation cover 14′ is similar to cover 14, except that it includes amirror image of the latch member 31 at the opposite end (i.e., latchmember 31′) rather than the hinge and spring arrangement found in cover14 opposite latch member 31. The additional locking notches 32′ withinsecond latch member 31′ are able to lock over a second protrusion 34′within bracket base 12 in the same way notches 32 lock over protrusion34. In most other respects, ligation cover 14′ is virtually identical toligation cover 14. The orthodontic bracket 10′ may simply be provided asa two-piece assembly, or it may result by first removing the integralligation cover 14 depicted in FIGS. 1A and 1B, such as by using ascalpel, and then replacing it with the removable ligation cover 14′depicted in FIG. 2. Such a procedure may be necessary in cases where itis difficult for the ligation cover 14 to flip open, in order toadequately expose the arch wire slot 16 such as due to a cramped toothposition. A kit may be provided comprising the integral, one-pieceorthodontic bracket 10 and an auxiliary ligation cover 14′ that may beoptionally used to ligate an arch wire in the event it becomes necessaryto remove ligation cover 14.

FIGS. 3A–3B depict a variation of the orthodontic bracket 10′ depictedin FIG. 2, with the main difference being that the orthodontic bracket10″ depicted in FIGS. 3A and 3B includes a flexible leash member 39interconnecting the bracket base 12 and ligation cover 14′. The mainpurpose of the leash member 39 is to prevent a practitioner frominadvertently misplacing the ligation cover 14′, or worse, accidentallydropping it down the patient's throat during ligation or adjustment. Forexample, the assembled bracket 10″ can be first attached to a tooth (notshown), followed by detachment of the ligation cover 14′, placement ofan arch wire 18 within the arch wire slot 16, and reattachment of cover14′, while reducing or eliminating the threat of a detached ligationcover 14′ being misplaced, dropped or allowed to fall down the patient'sthroat.

An alternative embodiment of a hinged orthodontic bracket is depicted inFIGS. 4 and 5. Orthodontic bracket 40 includes a bracket base 42 and aligation cover 44 attached to the base by a joint element 50. The base42 includes an arch wire slot 46 and an auxiliary slot 48 orientedtransversely to slot 46. Auxiliary slot 48 may be used in theconventional manner to assist in fixing an arch wire within the archwire slot 46, such as by means of wire or elastomeric ligatures. Theligation cover 44 is formed in a hood-like manner and is integrallyconnected to the joint element 50 by means of an integral hinge 52,which is advantageously a film hinge. The joint element 50 is similar indesign to the spring element 24 of the embodiment in accordance withFIGS. 1A and 1B, except that joint element 50 does not act as a spring,but merely as a connection between cover 44 and base 42. This is becausethe ligation cover 44 is not separately attached to the base 42 by anymeans other than the joint element 50. A recess 54 is advantageouslyprovided in the outside of the cover 44 so that the joint element 50 andthe cover 44 can nest together and form a single, smooth outer surfaceupon closing or locking the cover 44 with the base 42.

The base 42, ligation cover 44, and joint part 50 can either beintegrally molded in a single step, so as to yield an integral,one-piece orthodontic bracket, or else an end of the joint part 50opposite the integral hinge 52 may initially be detached from the base42 and thereafter attached to the base 42, e.g., by pushing the end ofjoint part 50 into a corresponding groove within the base 42 in aform-locking manner. In this way, the ligation cover 44 and joint part50 are insertably affixed to the base 42. In either embodiment, afurther integral hinge 53, such as a film hinge, may be provided in theregion of attachment between the joint part 50 and the base 42 so thatthe joint part 50, and thus also the ligation cover 44, can be pivotedabout the hinge 53 in order to facilitate rotation of the cover 44 overand onto the base 42 during ligation.

Peripheral locking notches (not shown) may be provided on an innersurface of the ligation cover 44 to assist in locking or clipping thecover 44 onto the base 42. An exit aperture 56 (FIG. 4B) is provided oneach side of the ligation cover 44 to allow complete closure of theligation cover 44 around an arch wire (not shown) placed within the archwire slot 46. An insertion slot 58 extending from the exit aperture 56to a lower edge of the ligation cover 44 permits the passage of the archwire into and out of each exit aperture 56 during opening and closing ofthe cover 44.

FIGS. 5–8 depict orthodontic brackets that are similar to the bracketsdepicted in FIGS. 1–2, except that the brackets of FIGS. 5–8 furtherinclude a bearing spring extending from the ligation cover and partiallyinto the arch wire slot when the ligation cover is in a locked positionso as to provide an alternative, or additional, means for providingdynamic active ligation of the arch wire as the tooth moves over timeinto proper alignment. Some embodiments further include under cuts orrecesses within an underside of the base to assist in adhering thebracket to a tooth. One of ordinary skill will readily appreciate,however, that the underside of the bracket base could alternatively betextured or roughened to promote better adhesion to the tooth.

FIGS. 5A–5C depict an orthodontic bracket 60 manufactured as a singlepiece from, e.g., a plastic material (e.g., by injection molding).Orthodontic bracket 60 includes a bracket base 62 shaped approximatelylike an anvil in cross section and a ligation cover 74 integrallyattached to the base 62 in an articulated manner. The bracket base 62includes a main arch wire slot 64 that opens upward for receipt of anarch wire (not shown) therein. As in the embodiment depicted in FIGS.1–2, the bracket base 62 may optionally include a reinforcement insert(not shown) to provide greater durability and wear resistance. Anyappropriate arch wire may be inserted into slot 64 and ligated using thecover 74.

The bracket base 62 further includes an upper end 66 next to the archwire slot 64, with a locking protrusion or edge 68 formed in a side ofthe upper end 66 distal to the arch wire slot 64. The locking protrusion68 is used to engage locking notches 78 formed with a curved latchelement 76 within ligation cover 74. Below edge 68 is an auxiliary archwire slot 70 that may be used to hold therein an auxiliary arch wire(not shown). The arch wires within both of slots 64 and 70 can byligated at the same time by the single action of simply closing orlocking the ligation cover 74 over the bracket base 62. Further down,the bracket base 62 includes a secondary recess 72, and a correspondingrecess 72′ on the other side, which can be used, if desired, to secureconventional ligatures to the base 62.

The ligation cover 74 forms a protective hood so as to substantiallycover the upper surface of the bracket base 62 and arch wire slot 64when in a locked position. The ligation cover 74 is approximatelykidney-shaped in cross section and is connected in one piece to the base62 by means of a first integral hinge 82, e.g., a film hinge. A springelement 84, similar to the spring element 24 depicted in FIGS. 1–2, butcurved approximately like an arc in cross section, is integrallyattached at one end to the bracket base 62 in an articulated manner bymeans of a first joint 86 and at another end to the ligation cover 74 bymeans of a second joint 88, both of which can be film hinges, i.e.,areas of locally reduced cross-sectional thickness.

As more particularly shown in FIG. 5C, the spring element 84 is designedand oriented so as to interact with the ligation cover 74 to yield asubstantially smooth and uniform outer surface when the cover 74 is in alocked position relative to the bracket base 62. Together, the cover 74and spring 84 form a hood-like, kidney-shaped protective shell over thebase 62. To facilitate nesting of the spring element 84 into theligation cover 74, a depression 90 (FIG. 1) is provided in an upper sideof the cover 74. The locking notches 78 provide for varying lockedpositions of the ligation cover 74 relative to the base 62 in order toapply varying levels of pressure to the arch wire.

A leaf spring 80 extends from an inner surface of the cover 74 and ispositioned so as to partially extend into the arch wire slot 64 when thecover 74 is in a locked or closed position relative to the base 62. Theleaf spring 80 is an example of a bearing spring. The purpose of theleaf spring 80 is to provide downward pressure onto an arch wirepositioned within arch wire slot 64. Because the leaf spring 80 is ableto compress or extend, depending on how completely the arch wire (notshown) is seated within the arch wire slot 64, the bearing spring 80comprises means for providing dynamic active ligation of an arch wireover time as the tooth to which the orthodontic bracket 60 is attachedis moved into proper alignment. The bearing spring 80, either alone orin combination with a flexible ligation cover, is able to absorbalignment energy from an arch wire initially bearing upward toward thebearing spring 80 and then incrementally release this energy over timeas the arch wire becomes more completely seated within the arch wireslot 64, to thereby provide dynamic active ligation of the arch wire(see FIGS. 12A and 12B). The pressure exerted by the bearing spring 80onto the arch wire can be adjusted by raising or lowering the ligationcover 74 relative to the base 62 by altering which of the lockingnotches 78 within the latch 76 engages the locking edge 68.

The base 62, cover 74, spring element 84, and bearing spring 80 can beintegrally molded as a single piece by injection molding an appropriateplastic material. In the alternative, the various pieces can beseparately molded and then joined together using heat, cement or othermechanical fixation means known in the art. The joint 86 between thespring element 84 and base 62 is preferably located approximatelyhalfway up the base 62, between its bottom and its upper side, while thejoint 88 between the spring 84 and ligation cover 74 is attached to thecover 74 so as to sit directly above the arch wire slot 64 when theligation cover 74 is closed (FIG. 5C). Each of the film hinges 82, 86and 88 advantageously extend across the entire width of the bracket base62 for maximum durability. The bearing spring 80 may also extend acrossthe entire width of the base 62, or any portion thereof, depending onthe desired stiffness.

As more clearly shown in FIG. 6A, the locking notches 78 may be shapedso as to form curved depressions therebetween, or they may be moreserrated or sharp-edged as shown in FIG. 6B. The shape of the lockingnotches 78 will typically depend on the shape of the correspondinglocking edge 68 within the upper side 66 of the base 62.

Spring element 84 operates to urge the ligation cover 74 to remain openwhile in an open position, and to remain closed while in a closedposition. As more particularly shown in FIGS. 5B and 5C, if the spring84 were not attached to the ligation cover 74 by hinge 88, a resultinghypothetical free end of spring 84 would rotate about the hinge 86interconnecting the spring 84 and the bracket base 62 and travel along ahypothetical arc A₂, which is defined by a radius R₂ having its originat said hinge 86. However, because the spring 84 is also affixed to theligation cover 74 by hinge 88, the end of the spring 84 attached to thecover 74 at hinge 88 is instead forced to travel along an arc A₁, whichis defined by a radius R₁ having its origin at hinge 82 interconnectingthe ligation cover 84 and the bracket base 62. In this way, the springelement 84 operates much the same way as the spring element 24 depictedin FIGS. 1A and 1B, because it is elastically distorted as the ligationcover 74 is rotated between the open and closed positions. What isdifferent is that spring element 84 is able to continue urging theligation cover 74 to remain closed with significant downward force evenwhen the ligation cover 74 is rotated into the closed, or locked,position. In this way, the ligation cover 74 is able to providecontinuous ligation pressure even when the locking notches 78 aredisengaged from the locking edge 68.

The spring element 84 is able to exert a significant closing force uponthe ligation cover 74 even when closed because the spring element 84remains partially tensioned, or elastically elongated, even afterrotating the cover 74 into the closed position. As shown in FIG. 5B, thetransition between where the spring 84 urges the cover 74 to move towardeither an open or closed position is in the region of distance X, whichis the maximum offsetting distance between arcs A₁ and A₂. As a resultof the relative locations of the points of origin of radii R₁ and R₂,the spring 84 does not completely relax as the ligation cover 74 isrotated into a closed position, but remains elongated by a distance Ybetween arcs A₁ and A₂. Due to the above-mentioned kinematics, thespring force exerted by spring element 84 does not go to zero when theligation cover 74 is closed, but is rather reduced by about 70% relativeto the maximum spring force in the region of distance X. Accordingly,the bearing spring 80, in combination with the continuous force exertedby the spring element 84, is able to provide active ligation of an archwire disposed within the arch wire slot 64 even when the locking notches78 do not engage the locking protrusion 68.

The ligation cover 74 is also able to provide passive ligation of asecond arch wire disposed within auxiliary arch wire slot 70, which isparallel to slot 64 but which opens laterally away from the main archwire slot 64 and out a side of the bracket base 62. As a result of theclosing force provided by the spring element 84, the ligation cover 74provides secure and reliable passive ligation of an arch wire locatedwithin auxiliary arch wire slot 70, even when the locking notches 78 donot engage the locking protrusion 68. Moreover, the forces exerted by asecond arch wire within auxiliary slot 70 would not include a forcevector of sufficient force to overcome the force of the spring element84 that urges the cover 74 to remain closed. In this way, the springelement 84 is able to provide an important safety feature in the eventthat the ligation cover 74 is inadvertently unlocked, such as by upwardpressure by the main arch wire at located within the main arch wire slot64.

FIGS. 7A–7C depict an embodiment of an orthodontic bracket 100 that issubstantially similar to the orthodontic bracket 60 depicted in FIGS.5A–5C, except that orthodontic bracket 100 further includes under cutswithin the bottom surface of the bracket base to enhance the ability ofthe orthodontic bracket to adhere to a tooth. This assists, for example,in those cases where the plastic used to manufacture the orthodonticbracket 100 is a non-stick material that resists adhesion by foreignmaterials.

As more particularly shown in FIG. 7A, the orthodontic bracket 100includes a bracket base 102 into which a pair of parallel under cuts 104have been formed. The under cuts 104 are inwardly enlarged so as to havea wider cross-section within the interior of base 102 then where theyopen at the bottom of the base 102. In this way, the cement or adhesiveentering under cuts 104 can mechanically interlock with the bracket base102 upon hardening. In this way, an adhesive will still be able tosecure the orthodontic bracket 100 to the tooth even if the adhesive isunable to form a strong chemical or adhesive bond with the plastic usedto form the orthodontic bracket 100. In all other respects, theorthodontic bracket 100 is substantially similar to the orthodonticbracket 60 depicted in FIGS. 5A–5C.

The orthodontic bracket 100 includes a ligation cover 101 that isintegrally attached to an upper end 106 of the bracket base 102 by meansof an integral hinge 103 (e.g., a film hinge). A spring element 105interconnects the ligation cover 101 with the bracket base 102 in orderto urge the ligation cover 101 to remain open while in an open position,and to remain closed while in a closed position. The spring element 105is attached at one end to the bracket base 102 by a base hinge 107 andat an opposite end to the ligation cover 101 by a cover hinge 108, bothof which may comprise film hinges. The kinematics of the forces betweenthe spring element 105 and the ligation cover 101 are substantiallysimilar to those described above with respect to orthodontic bracket 60.The ligation cover 101 further includes a curved latch element 109 thatfurther includes locking notches 110 designed to interact with aprotruding edge 112 of an upper end 114 of the bracket base 102. Abearing leaf spring 115 extends from an inner surface of the ligationcover 101 into an arch wire slot 116 within the bracket base 102 whilethe ligation cover 101 is in a closed or locked position. One notabledifference between orthodontic bracket 100 and orthodontic bracket 60 isthat the space 117 between the spring element 105 and the ligation cover101 in orthodontic bracket 100 is smaller than the corresponding spacein orthodontic bracket 60 such that upon closing the ligation cover 101,the space 117 is almost entirely eliminated as the spring 105 is broughttoward the surface of the ligation cover 101 (FIGS. 7B–7C). In contrast,a substantial space remains between the spring element 84, base 62 andligation cover 74 of the orthodontic bracket 60 depicted in FIGS. 5A–5C.As demonstrated in FIGS. 7B and 7C, the locking notches 110 provide forvarying degrees of closure of the ligation cover 101 relative to thebracket base 102. This allows an orthodontic practitioner to adjust thelevel of force exerted by the leaf spring 115 onto an arch wire (notshown) disposed within the arch wire slot 116.

FIG. 8 depicts an alternative orthodontic bracket 100′ that issubstantially identical to orthodontic bracket 100, except that thespring element 105 and the hinge 103 have been eliminated in favor of acurved latch element 109′ corresponding to, and comprising the mirrorimage of, the curved latch element 109 located distal to the springelement 105 of orthodontic bracket 100. In this way, the ligation cover101′ is detachable from bracket base 102′ such that a two-pieceorthodontic bracket 100′ is provided. A flexible leash element 111interconnecting the base 102′ and ligation cover 101′ may be provided toprevent the ligation cover 101′ from being inadvertently misplaced ordropped down the patient's throat during ligation or adjustment. Thecurved latch 109′ includes locking notches 110′, which are able toprovide variable locking positions relative to a second protrusion 112′in an upper end 114′ opposite to upper end 114.

FIGS. 9A–9D depict alternative bearing springs that may be employed toprovide dynamic active ligation from the ligation cover to an arch wiredisposed within an arch wire slot. For example, FIG. 9A depicts aserpentine spring 118 having a plurality (e.g., three) transitions ofcurvature, rather than the single curvature of the leaf spring 115 shownin FIGS. 7–8. In this way, the serpentine spring 118 will be able toelastically compress and elongate over a greater distance so as toprovide a greater range of dynamic active ligation of an arch wire. Thezig-zag spring 120 depicted in FIG. 9B similarly provides a larger rangeof compression and elongation compared to a simple leaf spring.

The coiled spring 122 depicted in FIG. 9C provides another alternativemeans for actively ligating an arch wire. The dual leaf springarrangement 124 depicted in FIG. 9D provides a two-stage bearing effectonto a ligated arch wire. In particular, a longer leaf spring 126extends more fully into the arch wire slot and will continuously providea ligating force to an arch wire disposed therein. A shorter leaf spring128 may provide additional ligation pressure onto an arch wire that isless fully seated within the arch wire slot, depending on how far thearch wire is from being fully seated. In this way, greater ligationpressure can be applied to an arch wire that is less fully seated, suchas where the orthodontic bracket is attached to a tooth that isparticularly misaligned. In this way, the dual leaf spring 124 is ableto exert significantly greater alignment pressure onto a more poorlyaligned tooth, and then relax as the tooth becomes partially realigned.

FIGS. 10A–10B demonstrate the ease with which the orthodontic bracket100 can be opened and closed without the need for special tools orcomplicated techniques. As shown in FIG. 10A, the ligation cover 101 caneasily be opened by means of a person's fingernail 130. FIG. 10B depictsthe use of a simple dental tool or pick 132, which is commonly used byall dentists, to open ligation cover 101. It is readily apparent thatthe cover 101 is easily closed by a person's finger.

FIGS. 11A–11B depict alternative numbers of under cuts that may beincluded within a bracket base 102″ to promote adhesion to a tooth. FIG.11A depicts a single trapezoidal under cut 104′, while FIG. 11B depictsthree parallel trapezoidal under cuts 104″. It will be appreciated thatthe under cuts within an orthodontic bracket base may assume any desiredshape or orientation. In general, the greater the number of under cuts,the greater will be the ability for cement or glue to mechanicallyadhere to the bottom of the orthodontic bracket base. Moreover, allthings being equal, under cuts that are tapered such that they becomemore enlarged toward the interior of the bracket base (see FIGS. 7–8 and10–11) will provide greater mechanical retention than those which do nothave such a taper. Of course, one of ordinary skill will realize thatthere are any number of design features that could be used to promoteadhesion of the orthodontic bracket to a tooth, including a textured orroughened under surface, or any other adhesion promoting designs knownin the art.

FIGS. 12A–12B demonstrate the concept of dynamic active ligation by anorthodontic bracket 100″. In particular, FIG. 12A depicts a serpentinebearing spring 118 disposed on ligation cover 101″ in a compressed stateand bearing down on an arch wire 134 that is not fully seated within thearch wire slot 116. Over time, as the arch wire 134 becomes more fullyseated within the arch wire slot 116 (more precisely, as the tooth andassociated orthodontic bracket 100″ move toward the arch wire 134), thebearing spring 118 elongates and continues to provide active ligationpressure onto the arch wire 134. In this way, the bearing spring 118 isable to provide continuous ligation pressure without the need toreadjust the position or tightness of the ligation cover 101″ relativeto the base 102. The bearing spring 118 is able to initially absorbmechanical energy that is transferred from the impartially seated archwire 134 depicted in FIG. 12A. This mechanical energy is transferred,albeit in a dampened state, to the tooth being realigned so as to urgethe tooth into proper alignment. Over time, as the tooth moves intoproper alignment, the mechanical energy stored by bearing spring 118 isincrementally released or reduced. The absorption of arch wire energy bybearing spring 118 also provides a dampening effect on the amount offorce that would otherwise be exerted by the arch wire 134 onto thetooth being realigned, thus providing greater comfort and less pain tothe patient.

Reference is now made to FIGS. 13–15, which depict an integrally-moldedone-piece orthodontic bracket 140 that includes a hinged ligation coverwith a special safety locking device. As more particularly depictedtherein, the orthodontic bracket 140 includes a bracket base 142 thatsits atop a bonding platform 144 and that includes a main arch wire slot146 configured to receive an arch wire 147. An auxiliary arch wire slot148, parallel to, but opening in a direction generally perpendicular to,a longitudinal axis of the arch wire slot 146 is provided for theoptional inclusion of an auxiliary arch wire (not shown).

The ligation cover 150 is hingedly attached to the bracket base 142 andconfigured so as to cover the arch wire slot 146, an upper side 150 ofthe bracket base 142, and the auxiliary arch wire slot 148 in a singleclosing or locking action. The ligation cover 150 includes a curvedlatch member 152 having a generally trapezoidal tongue 154 extendingtherefrom. The trapezoidal tongue 154 is configured so as to beslideably retained within an angled key way 156 extending outward fromthe auxiliary arch wire slot 148. The locking tongue 154 is able to snapover an outer protrusion 153 of an upper side 151 of the bracket base142 due to the flexibility of the ligation cover 150, which allows thelatch 152 to flex outwardly and away from the hinge region (discussedbelow). Once the locking tongue 154 has flexed outwardly and passed overand around the protrusion 153 so as to line up with the angled key way156, the spring-like resilience of the ligation cover 150 causes thelatch member 152 to retract and return to its original conformation,thereby pulling the locking tongue 154 partially into the angled key way156 (FIGS. 14B–15A). The manner in which the trapezoidal tongue 154 andangled key way 156 serve to provide a more secure locking mechanism forretaining ligation cover 150 in a locking arrangement with bracket base142 will be discussed hereinafter.

The ligation cover 150 is hingedly attached to the bracket base 142 bymeans of an integral hinge 162 (e.g., a film hinge). A spring member 160interconnects the ligation cover 150 and the bracket base 142 in orderto provide a desired resistance to inadvertent closing and opening ofthe ligation cover 150. As in other embodiments, the spring member 160urges the ligation cover 150 to remain open while in an open position,and to remain closed while in a closed position. Positive force isrequired to selectively rotate the ligation cover 150 from a closed toan open position and from an open position to a closed position. Thespring 160 is generally curved and is integrally connected to thebracket base 142 by means of an integral hinge 164 and to the ligationcover 150 by means of integral hinge 166, both of which mayadvantageously be film hinges. A bearing protrusion 158 extends from theligation cover 150 and partially into or above the arch wire slot 146when the ligation cover 150 is closed relative to the bracket base 142in order to apply ligation pressure to the arch wire 147 and therebyprovide active ligation.

The interaction of the locking tongue 154 and the angled key way 156serve to provide a more secure locking mechanism that preventsinadvertent unlocking and opening of the ligation cover 150. Inparticular, in the event that the arch wire 147 is not completely seatedwithin the arch wire slot 146, but pushes against the bearing protrusion158 of the ligation cover 150 with sufficient force to cause the cover150 to bulge upwardly relative to the bracket base 142, rather thancausing the tongue 154 to withdraw from the angled key way 156, whichcould possibly result in undesired disengagement of the latch member152, the locking tongue 154 is instead pulled more deeply into theangled key way 156, thereby tightening the locking mechanism (FIGS. 15Aand 15B).

In general, a first side of the locking tongue 154 makes slidableabutting contact with an upper surface 157 of the locking key way 156while the ligation cover 150 is in a locked position relative to thebracket base 142. An opposite side of the locking tongue 154 makesslidable abutting contact with an angled bearing surface 159 of theangled key way 156. In this way, the locking tongue 154 is angularlyrestrained so that it is only able to move along an angled vector Vdepicted in FIG. 14B. The vector V is parallel to the angle of thetrapezoid that defines the locking tongue 154 and the angle of inclineof angled key way 156. The locking tongue 154 is thereby prevented fromflexing outward when the ligation cover 150 bulges away from the bracketbase 142. Thus, when upward pressure is exerted by the arch wire 147 tothe ligation cover 150, the ligation cover 150 effectively shortens,rather than lengthens, relative to the length of the bracket base 142such that the ligation cover 150 can only pull the locking tongue 154more deeply into the angled key way 156. In short, the restrainingaction by the key way 156, coupled with an effective shortening of theligation cover 150, reliably prevents the locking tongue 154 from movingdownward along vector V so as to inadvertently slide out from the angledkey way 156. Instead, upward pressure by the arch wire 147 can only havethe effect of tightening, rather than loosening, the locking forcebetween the locking tongue 154 and the angled key way 156, as shown inFIGS. 15A and 15B.

When it is desired to open or unlock the ligation cover 150, anappropriate tool, such as a fingernail or curved dental tool of the typedepicted in FIG. 10B, can be used to engage a protrusion 155 extendingfrom the latch member 152 (FIG. 14B) so as to flex the latch 152 andassociated locking tongue 154 outwardly and out of the angled key way156. Thus, the flexibility of the ligation cover 150 allows the curvedlatch 152 to either be released out of the angled key way 156 whenpulled outwardly by an appropriate tool or to be pulled more deeply intothe angled key way 156 when an arch wire pushes upward causing theligation cover 150 to bulge outwardly and away from the bracket base142.

Finally, as more particularly shown in FIG. 13C, the underside ofplatform 144 within the bracket base 142 includes a recessed area 168and protrusions 169 disposed within the recessed area 168. The purposeof the recessed area 168 and protrusions 169 is to provide increasedsurface area, as well as mechanical interlocking with an adhesive, whichserves to better adhere the platform 144 to a tooth. The increasedsurface area provides greater adhesion between the platform 144 and thetooth so as to prevent the bracket from pulling away from the tooth in alabial direction. Moreover, the protrusions 169 provide mechanicalresistance to lateral movement of the orthodontic bracket 140 relativeto the tooth surface.

FIGS. 16A–16B depict a two-piece orthodontic bracket 140′ that issimilar to the orthodontic bracket 140 depicted in FIGS. 13–15. The maindifference is that orthodontic bracket 140′ includes a ligation cover150′ that is neither hingedly attached to, nor integrally formed as asingle piece with, the bracket base 142′. Instead, the ligation cover150′ is a separate and fully detachable piece. As in orthodontic bracket140, the ligation cover 150′ includes a trapezoidal locking tongue 154that fits and locks within an angled key way 156. Because the ligationcover 150′ is not hinged or otherwise connected at the other end, italso includes a second trapezoidal locking tongue 154′ configured tolock with, and be received within, an angled key way 156′ such that theyinteract together in the same way as locking tongue 154 and angled keyway 156. As above, the locking tongue 154 is restrained by the confinesof the angled key way 156 so that it is only capable of moving along afirst vector V₁, which corresponds to the angle of the trapezoid thatdefines the locking tongue 154 and the angle of incline of angled keyway 156. Similarly, locking tongue 154′ is restrained by the confines ofangled key way 156′ such that it can only move along a second vector V₂corresponding to the angle of the trapezoid of locking tongue 154 andthe angle of incline of angled key way 156′. Accordingly, the ligationcover 150′ includes dual safety locking features, one on either side,that serve to tighten the connection between the ligation cover 151′ andthe bracket base 142′ in the event that upward pressure from an archwire 147 causes the ligation cover 150′ to bulge upwardly and away fromthe bracket base 142′.

The bracket base 142′ also includes a second auxiliary arch wire slot148′, which opens up through angled key way 156′. Thus, the orthodonticbracket 140′ includes three initially open arch wire slots that can bequickly and easily ligated in a single step by simply attaching theligation cover 151′ over the bracket base 142′. An optional leash member(not shown) may be included to prevent inadvertent loss of the ligationcover 150′.

FIGS. 17A–17B depict another alternative embodiment an orthodonticbracket according to the invention. In particular, FIGS. 17A and 17Bdepict an orthodontic bracket 170 that is substantially similar to theorthodontic bracket 140 of FIGS. 13–15, except that bracket 170 does notinclude a spring member 160. Instead, a ligation cover 174 is integrallyattached to the bracket base 172 by means of a single integral hinge 176(e.g., a film hinge). This allows the ligation cover 174 to rotate morefreely between an open and closed position and with less force than isrequired to open and close the ligation cover 150 depicted in FIGS.13–15. In most other respects, orthodontic bracket 170 is similar toorthodontic bracket 140.

For example, the orthodontic bracket 170 includes the same safetylocking features as orthodontic bracket 140, including a trapezoidallocking tongue 178 that is configured to slidably fit within an angledkey way 179 within the bracket base 172. In addition, a bearingprotrusion 177 extends downwardly from the ligation cover 174 and ispositioned to extend partially into an arch wire slot 175 when theligation cover 174 is in a closed and locked position relative to thebracket base 172. An auxiliary arch wire slot 173 is located next to theangled key way 176 for receipt therein of an auxiliary arch wire (notshown) that can be ligated in a single step, at the same time as archwire 147, by closing the ligation cover 174 so that the locking tongue178 is inserted into the angled key way 179. A second auxiliary archwire slot 171 may optionally receive a second auxiliary arch wire (notshown) that can be ligated using convention ligatures (not shown).

FIGS. 18A–18B depict an orthodontic bracket 180 that is similar toorthodontic bracket 170 of FIGS. 17A–17B, except that a bracket base 182and ligation cover 184 are formed separately and then hingedly attachedtogether by means of a conventional hinge 186, such as by means of ahinge pin 188 passing through corresponding recesses within the bracketbase 182 and ligation cover 184. The orthodontic bracket 180 alsoincludes the safety locking feature described in the precedingembodiments, including a locking tongue 185 that fits within an angledkey way 187 within the bracket base 182. The bracket base 180 includesauxiliary arch wire slots (not labeled).

FIG. 18C depicts an orthodontic bracket 190 that is substantiallysimilar to the preceding embodiments, except that the ligation cover 194and bracket base 192 are separately formed and then connected togetherby means of a separate joint or connection feature 196. The connectionfeature 196 may comprise, for example, an elastomeric cement or glue, orfibers or a fabric integrally embedded within an end of the ligationcover 194 and a corresponding end of the bracket base 192, both of whichwould yield a flexible joint. In the alternative, the connection feature196 may comprise, a rigid cement or glue such that the connectionfeature 192 will not comprise a flexible joint. In that case, theligation cover 194 will need to be sufficiently flexible such that itcan be opened and closed without the aid of a flexible joint or hingearea.

As with previous embodiments, the orthodontic bracket 190 includes thesafety locking feature described above, including a locking tongue 197and an angled key way 198. The ligation cover 194 is also able toselectively ligate and release a pair of arch wires 147, 147′ by closingand opening the ligation cover 194 relative to the bracket base 192. Athird arch wire 147″ can be optionally inserted into a second auxiliaryarch wire slot 199 if desired. Because the ligation cover 194 does notserve to enclose auxiliary arch wire slot 199, other ligation means,such as conventional ligatures, would be necessary to ligate theauxiliary arch wire 147″.

FIGS. 19A–19B depicts an orthodontic bracket 140″ that is similar to theorthodontic bracket 140 depicted in FIGS. 13–15, but which includes anarch wire slot 146′ that is offset at an angle such that it is notperpendicular to the bottom of the bracket base platform 144. Acorresponding angled bearing protrusion 158′ extends from the ligationcover 150″ and is situated so as to be partially inserted into the archwire slot 146′ when the ligation cover 150″ is closed in order to applyligation pressure to the arch wire 147 and thereby provide activeligation. An angled arch wire slot may be desirable in order to providedifferent torquing forces to straighten a particular tooth compared toan arch wire slot that is not angled. In this particular case, theinclusion of an angled; arch wire slot results in an orthodontic bracket140″ having a lower profile than orthodontic bracket 140. In most otherrespects, orthodontic bracket 140″ is substantially similar toorthodontic bracket 140.

FIGS. 20A–20B depict an alternative embodiment of an orthodontic bracketaccording to the invention. The orthodontic bracket 200 depicted in20A–20B differs from orthodontic bracket 140 in the manner in which theligation cover and spring are attached to the bracket base. Instead ofbeing connected by integral hinges, the ligation cover 204 is hingedlyattached to the bracket base 202 by means of a conventional pin hinge206. A spring member 208 is integrally molded with, and connected to,the ligation cover 204 by means of an integral film hinge 210 at oneend, and hingedly attached to the bracket base 202 by means of aconventional pin hinge 212 at an opposite end. In this way, the ligationcover 204 and spring 208 can be injection molded as a single piece inone step and thereafter attached to a separately molded bracket base 202by means of the aforementioned conventional pin hinges 206 and 212. Oneof ordinary skill in the art will readily appreciate, however, that thespring member 206 could alternatively be attached to the ligation cover204 in any appropriate manner, such as by means of flexible cement orglue or a conventional pin hinge. One of ordinary skill in the art willbe able to select whatever attachment means is appropriate for aparticular manufacturing method.

FIGS. 21A–21C depict an orthodontic bracket 230 according to theinvention that includes a bracket base 232 and ligation cover 234 thatare initially molded from different types of plastics and then joined orfused together, such as by a two-color molding process. Even though theligation cover 234 and bracket base 232 are initially molded fromdifferent types of plastics, they can be fused together to form anintegral, one piece orthodontic bracket 230 in which the ligation cover234 is hingedly attached to the bracket base 232 by means of an integralhinge 236 (e.g., a film hinge). The bracket base 232 includes a mainarch wire slot 233 for receipt of an arch wire 240 therein. As seen inFIGS. 21B and 21C, the bracket base 232 further includes under cuts 249for improved adhesion to a tooth and two auxiliary arch wire slots 248and 248′ opening on either side of the bracket base 232.

The ligation cover 234 further includes a locking clasp 242 that wrapsaround a nose 244 of an upper side 246 of the bracket base 232. Abearing protrusion 238 extends from the underside of the ligation cover234 so as to partially extend into, or at least over, the arch wire slot233 when the ligation cover 234 is in a closed or locked positionrelative to the bracket base 232. As shown in FIG. 21C, the flexibilityand resiliency of the ligation cover 234 permits it to flex upwardly andabsorb mechanical energy from the arch wire 240 when not entirely seatedwithin the arch wire slot 233. In this way, the flexible ligation cover234 is able to provide dynamic active ligation over time as the archwire 240 becomes more fully seated within the arch wire slot 233.

It will be readily appreciated that the orthodontic bracket 230 of FIGS.21A–21C could be injection molded from a single materials, such as aplastic material, to form a one-piece bracket that is integrally formedin a single step.

FIG. 22 depicts an orthodontic bracket 230′ that is a variation of theorthodontic bracket 230 of FIGS. 21A–21C in that it includes a shorterligation cover 234′ having a curved locking clasp 242′ of reduced sizethat can be locked to the bracket base 232′ by insertion of the lockingclasp 242′ into a locking slot 231 formed in an upper side 246′ of thebracket base 232′. In most other respects the orthodontic bracket 230′of FIG. 22 is substantially similar to the orthodontic bracket 230 shownin FIGS. 21A–21C. Because the ligation cover 234′ is of shorter length,it will tend to have less flexibility than ligation cover 234 oforthodontic bracket 230, all things being equal.

As depicted in FIG. 22, the ligation cover 234′ and bracket base 232′comprise different types of plastic materials, which may be separatelyformed and then joined together by way of a two-color molding process.It will be readily appreciated that the orthodontic bracket 230′ of FIG.22 could also be injection molded from a single plastic material to forma one-piece bracket that is integrally formed in a single step.

FIGS. 23A–23C depict an orthodontic bracket 250 that is initially formedin two pieces and then joined or fused together, such as by two-colormolding. In particular, the orthodontic bracket 250 includes a bracketbase 252 that may be advantageously manufactured from a harder, moredurable plastic, while the ligation cover 254 may be advantageouslyformed from a more flexible and resilient plastic. Unlike previousembodiments, the ligation cover 254 includes no locking clasp or latch;instead, it merely terminates with a generally flat end 256 that slidesor tucks into a locking slot or region underneath a locking lip oroverhang 258 disposed at, or formed within, an upper end of the bracketbase 252. Thus, the ligation cover 254 is able to become locked andunlocked primarily due to its having flexibility, rather than having aparticular locking feature, such that it can be flexed outwardly fromthe bracket base 252 and withdrawn from the locking slot defined by theoverhang or lip 258, such as by means of a conventional dental pick (notshown). Deflection of the ligation cover 254 away from the bracket base252′ effectively shortens the length of the cover 254, therebyfacilitating selective insertion and withdrawal of the end 256 relativeto the locking slot defined by overhang 258. This flexibility alsoprovides the ability of the ligation cover 254 to absorb mechanicalenergy from an arch wire 259 bearing upward toward the cover 254. Overtime, as the arch wire 259 becomes more fully seated within the archwire slot, the resiliency of the ligation cover 254 causes it to releasethe stored mechanical energy, which is transferred to the arch wire 254and/or tooth during realignment.

It will be readily appreciated that the orthodontic bracket 250 of FIGS.23A–23C could also be injection molded from a single plastic material toform a one-piece bracket that is integrally formed in a single step. Inthe case where the bracket base 252 and/or the ligation cover 254 aremade from metal, one end of the base and a corresponding end of theligation cover can be affixed together by means of welding, one or morescrews, rivets, pins, a mechanical hinge or other attachment means knownin the art.

FIGS. 24A–24B depict a two-piece orthodontic bracket 260 that includes abracket base 262 and a ligation cover 264 that are separately formed andthen mechanically attached together. The bracket base 262 includes aslot 268 into which a corresponding tongue 266 of the ligation cover 264is able to be inserted. The tongue 266 is advantageously sized relativethe width of the slot 268 such that the tongue 266 will form a tight fitwithin the slot 268. In this way, the ligation cover 264 may beinhibited or prevented from becoming detached from, or sliding relativeto, the bracket base 262. In an alternative embodiment, the tongue 266may be sized relative to the slot 268 so that the tongue may be slidablydisposed within the slot 268. Glue, welding or other securing meansknown in the art may be employed to affix the tongue 266 within the slot268.

The ligation cover 264 may be manufactured from any appropriatematerial, e.g., metal as depicted in FIGS. 24A and 24B, so long as it issufficiently flexible so that the ligation cover 264 is able to flexsufficiently so as to be selectively locked or unlocked within a lockingslot or region beneath a locking lip or overhang 270 formed within thebracket base 262. As in previous embodiments, the ligation cover 264 mayadvantageously include a bearing protrusion 272 that extends partiallyinto, or at least above, a main arch wire slot 274 within the bracketbase 262 when the ligation cover 264 is in a closed position relative tothe bracket base 262. The bearing protrusion 272 makes abutting contactwith an arch wire 276 disposed within the main arch wire slot 274 so asto provide active ligation. The flexible ligation cover 264 can absorband then release mechanical energy over time from the arch wire 276, asdepicted in FIG. 24B and as discussed above with respect to previousembodiments. The bracket base 262 may advantageously include recesses278 within an underside for improved adhesion to a tooth.

FIGS. 25A–25B depict a two-piece orthodontic bracket 280 in which aligation cover 284 is hingedly attached to a bracket base 282 by meansof a conventional pin hinge 286. The ligation cover 284 may be made fromany material, such as metal as depicted in FIG. 25B, or plastic (notshown). The ligation cover 284 is also shaped so as to function in amanner similar to the special locking feature described above, which isable to tighten and form a more secure lock between the ligation cover284 and the bracket base 282 as the ligation cover 284 is caused tobulge outwardly from the bracket base 282 as a result of upward pressurefrom an arch wire 288. The ligation cover is also designed so as toligate both the main arch wire 288, as well as an auxiliary arch wire287. The bracket base 282 includes recesses 289 for enhanced adhesion.

FIG. 25C depicts an orthodontic bracket 280′ that is a variation of theorthodontic bracket 280 of FIGS. 25A and 25B, except that the ligationcover 284′ is not hingedly attached to the bracket base 282′, but israther separate and completely removable. The ligation cover 284′ isshaped so as to include special trapezoidal locking features 285 and285′, similar to those described above in previous embodiments, oneither side of the cover 284′, which tighten as the ligation cover 284′is flexed upwardly away from the bracket base 282′ by means of an archwire that is not completely seated with a main arch wire slot. Theligation cover 284′ is further able to ligate two auxiliary arch wires287 and 287′ at the same time as the main arch wire 288 in a singleligation step of attaching the ligation cover 284′ to the bracket base282′. When the ligation cover 284′ is removed from the bracket base282′, all three of arch wire slots 288, 287 and 287′ are completely openand able to receive an arch wire therein.

FIGS. 26A and 26B depict an orthodontic bracket 290 that is manufacturedin two or three pieces and then assembled to form an orthodontic brackethaving a hinged ligation cover 294 that is affixed to a bracket base292. The ligation cover 294 is manufactured from either a singlematerial, such as plastic or metal, or from two separate materials, asdepicted in FIG. 26B, such as a plastic material for a hinged portion296 that opens and closes so as to ligate an arch wire 298, and a metalfor an attachment portion 300. One side of the attachment portion 300slides into a slit 302 formed within the bracket base 292, and anotherside is crimped around, or otherwise affixed to, the hinged portion 296,such as by means of an appropriate glue or cement. The attachmentportion 300 may either be slidably or fixedly attached to the bracketbase 292. The ligation cover 294 further includes a film hinge 304within the hinged portion 296. This allows the hinged portion 296 of theligation cover 294 to pivot or rotate about a film hinge located in theligation cover itself, rather than at a joint between the ligation coverand bracket base, as in previous embodiments. The bracket base 292 mayadvantageously include recesses 306 for improved adhesion of the bracketbase 292 to a tooth. The hinged portion 296 is advantageously flexibleto assist inserting an end of the hinged portion distal to the hinge 304under a corresponding lip, overhang or other locking feature associatedwith the bracket base 292.

Although the foregoing embodiments are discussed and depicted as beingable to selectively ligate and release an arch wire by locking andunlocking (or opening and closing) of the ligation cover relative to thebracket base, it will be appreciated that the ligation cover can bepermanently affixed to the bracket base, if so desired, at any timethrough the application of an appropriate glue or cement material at ornear the clasp, latch or other locking mechanism between the ligationcover and bracket base.

C. Summary of Improved Structural and Functional Features.

The exemplary orthodontic brackets described in the preceding sectioninclude one or more structural and/or functional features that arebelieved to be improvements over conventional orthodontic brackets. Amore focused summary will now be provided in order to better appreciatethe advantages of such improvements.

1. Orthodontic Brackets with Ligation Covers that Incorporate a FilmHinge.

A first improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooth, aligation cover, and a film hinge about which at least a portion of theligation cover can rotate so as to permit selective locking andunlocking of the ligation cover in order to ligate an arch wire receivedby the bracket base. As set forth above, the term “film hinge” refers toa local area of reduced cross-sectional thickness that facilitatespreferential localized bending of an article or device at the region ofthe film hinge. In the context of the ligation cover of an orthodonticbracket, a film hinge permits the cover to rotate or pivot about thefilm hinge such that the film hinge defines the origin of the radius ofthe arc or rotation of the ligation cover. In this way, the film hingeprovides a definite point or line about which the ligation cover willalways rotate, which reduces or eliminates unwanted bending stresseselsewhere in the cover (or place of attachment to the bracket if otherthan at the film hinge itself).

Moreover, a reduced cross-section within a resilient plastic materialyields a living hinge that can be rotated back and forth a number oftimes without becoming fatigued to the point of premature breakage. Ofcourse, one of ordinary skill will readily appreciate that the ligationcover of an orthodontic bracket is rarely opened and closed more than afew times over the lifetime of the bracket, which includes installingthe bracket, ligating an arch wire therewithin, and subsequentadjustments if needed. Thus, a film hinge can be employed in ligationcovers made of other materials such as metals and more rigid plastics.

Orthodontic brackets that incorporate a film hinge may manufactured as asingle integral piece (see FIGS. 1, 4, 5, 7, 10, 12–15 and 17) orinitially formed as two pieces that are joined or fused together usingtwo-color molding of dissimilar plastics (see FIGS. 20–22). They maycomprise two or more distinct pieces and/or materials that aremechanically attached together (see FIG. 26). The film hinge may belocated at the location where the ligation cover is attached to thebracket base, or it may be located elsewhere. The bracket base maycomprise any desired material of acceptable durability, such as metal,ceramic or rigid plastic, while the cover may comprise any desiredmaterial of acceptable flexibility and resilience, such as plastic ormetal. A ligation cover that includes a film hinge may be locked orattached to the bracket base using any locking or attachment mechanismdescribed herein or known in the art. The ligation cover may cover allor only a portion of the upper surface of the bracket base. Anorthodontic bracket may include one or a plurality of film hinges asdesired.

2. Orthodontic Brackets Incorporating an Arch Wire Bearing Spring withinthe Ligation Cover.

A second improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooth, aligation cover, and a bearing spring extending downward from theligation cover that is capable of being compressed by an arch wire thatis not entirely seated within a slot or other arch wire retention meansassociated with the base so as to absorb mechanical energy from the archwire. Such mechanical energy is then transferred to the tooth and/orback to the arch wire over time during realignment of the tooth, duringwhich the initially compressed spring expands or extends so as tomaintain continuous pressure onto the arch wire, which over time tendsto become better seated relative to the bracket base. In this way, thebearing spring provides for dynamic active ligation of an arch wireduring tooth realignment. Exemplary arch wire bearing springs areillustrated in FIGS. 5, 7–10, 12. In this way, the bearing spring yieldsan orthodontic bracket that is able to provide dynamic active ligationof an arch wire over time as the arch wire moves relative to theligation cover and becomes better seated within the arch wire slotduring tooth realignment.

The ligation cover may be integrally connected to the bracket base, suchas by being injection molded as a single piece or being joined togetherby two-color molding. Alternatively, the ligation cover may becompletely separate and detachable from the bracket base. The base canbe any rigid or durable material, such as metal, plastic or ceramic,while the cover can be any flexible and resilient material such asplastic or metal. The bearing spring may my integrally formed with theligation cover, and therefore comprise the same plastic or metalmaterial, or it may comprise a different material than the cover, suchas a metallic bearing spring having increased wear resistance whencontacted by an arch wire that is attached to the ligation cover.

3. Spring Action from Ligation Cover to Wire for Dynamic ActiveLigation.

A third improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a toothand a ligation cover that includes means for absorbing mechanical energyfrom an arch wire and then releasing such energy over time back to thearch wire and/or a tooth during tooth realignment. The arch wire bearingspring described in the immediately preceding section constitute anexample of means for absorbing and releasing mechanical energy from thearch wire in order to provide for dynamic active ligation during toothrealignment. In is also within the scope of the invention to providealternative means for absorbing and releasing mechanical energy from thearch wire, such as a ligation cover that has sufficient flexibility andresiliency so that it is able to temporarily deform or deflect andabsorb energy from an arch wire pressing upwards against the cover.Thereafter, this stored mechanical energy is released back to the archwire and/or tooth in order to urge migration of the tooth into properalignment and better seat the arch wire in the slot. Examples ofligation covers that are explicitly depicted as having absorbed archwire energy are include FIGS. 15B, 21C, 23C and 24B, although otherembodiments are described as optionally or explicitly providing thisfunction.

In the case where a flexible cover is relied upon to provide the solemeans of providing dynamic active ligation of the arch wire, it will bepreferable for the ligation cover to be attached to the bracket base ina manner so that the ligation cover does not slide relative to thebracket base during selective ligation and release of the arch wire. Itis more preferably for the ligation cover to be hingedly attached at oneend by a hinge feature that permits the ligation cover to rotate aboutthe hinge.

The orthodontic bracket may comprise any appropriate material(s) and maybe a one- or multi-piece bracket.

4. Orthodontic Bracket that Includes a Deformable Ligation Cover toFacilitate locking and Unlocking.

A fourth improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooth, alocking slot, stationary lip, overhang or other locking clasp associatedwith the base for slidably receiving therein an end of a flexibleligation cover, and a ligation cover fixed to the bracket base at oneend and having sufficient flexibility and resilience so as to beslidably inserted and removed from the locking clasp associated with thebracket base. Examples of such brackets are depicted in FIGS. 23, 24 and26.

The bracket base and ligation cover may comprise any appropriatematerial, such as metal, plastic or ceramic. They may be formed as anintegral, one-piece bracket, or they may be separately formed and thenjoined together, such as by mechanical means, adhesion or being fusedtogether (e.g., two-color molding of two separately molded plasticparts). The flexible ligation cover may or may not be hinged relative tothe bracket base, such as by a film or pin hinge.

5. Spring for Providing Resistance to the Rotation of a Ligation CoverAbout a Hinge.

A fifth improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooth, aligation cover hingedly attached to the base, and a spring element thatinterconnects the bracket base and ligation cover and urges the ligationcover to remain open while in an open position and/or to remain closedwhile in a closed position relative to the bracket base. Examples ofspring devices or elements that provide the afore-mentioned function areillustrated in FIGS. 1, 5, 7, 10, 12–15 and 20. It will be appreciatedthat other spring designs and arrangements relative to the bracket baseand ligation cover, in addition to those explicitly depicted in thedrawings, are contemplated and within the scope of the invention.

The bracket base, ligation cover and spring may comprise any appropriatematerial, such as metal, plastic or ceramic. The spring element may beattached to the bracket base and ligation cover by any appropriatemeans, such as by being integrally molded thereto, through the use of anadhesive (e.g., chemical or light curable), two-color molding or othermethods of fusing the spring between the cover and base (e.g., bywelding plastic or metal pieces together), or by attachment bymechanical hinges.

6. Ligation Cover Biased Toward Remaining in an Open or Closed Position.

A sixth improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooth, aligation cover hingedly attached to the base, and spring means forurging the ligation cover to remain open while in an open positionand/or to remain closed while in a closed position relative to thebracket base. The spring element interconnecting the bracket base andligation cover described in the immediately preceding sectionconstitutes an example of means for urging the ligation cover to remainopen and/or closed. In is also within the scope of the invention toprovide alternative means for urging the ligation cover to remain openand/or closed. Examples include elastomeric hinges and resilientmaterials that have elastic memory (see FIG. 18C). For example, one ormore elastomeric spring elements may be disposed between the ligationcover and bracket base in a manner so as to either bias the ligationcover toward remaining in a closed position or toward remaining in anopen position. Whether an elastomeric spring element will tend to biasthe ligation cover into remaining in an open or closed position willdepend on its location relative to the ligation cover and base.

Materials that have “elastic memory” include materials whose molecularstructure resists stretching, bending or other forms of deformation inthe short term, such as for a few second or minutes, but which willrelax and assume the new, deformed position and resist being deformedinto a new position, even the original position. One of ordinary skillin the art will be able to select an appropriate material having said“elastic memory” function.

The bracket base and ligation cover may comprise any appropriatematerial, such as metal, plastic or ceramic. They may be formed as anintegral, one-piece bracket, or they may be separately formed and thenjoined together, such as by adhesion using an elastomeric material or amaterial having elastic memory.

7. Two-Color Molding of Bracket Base and Ligation Cover Using DifferentTypes of Plastics.

A seventh improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooththat is molded using one type of plastic and a ligation cover that ismolding using another type of plastic and which has been fused orotherwise affixed to the bracket base using a two-color molding process.Employing two-color molding permits the bracket base to be manufacturedfrom a first plastic material that is advantageous for use in makingbases and the ligation cover to be make from a second plastic materialthat is advantageous for use in making covers.

For example, it is generally desirable for the bracket base to be rigidand durable so as to remain affixed to a tooth, while resisting beingdeformed or damaged by the forces applied thereto by one or more archwires. Flexibility is typically not beneficial to the operation andfunction of the bracket base. On the other hand, it is generallydesirable for the ligation cover to be more flexible and resilient,e.g., to permit the cover to be locked and unlocked relative to the baseand/or to absorb, store and release mechanical energy from the archwire, so as to provide dynamic active ligation of the arch wire. If aspring element is used to provide additional resistance to opening orclosing of the ligation cover, it may be integrally manufactured fromthe same plastic used to make either the bracket base or the ligationcover, or it may optionally be molded using a third type of plasticmaterial and then attached to the base and cover using two-colormolding.

Based on the advantages of using two-color molding, which become readilyapparent when reading the present disclosure, one of ordinary skill inthe art will be able to select appropriate plastic materials for use inmanufacturing an orthodontic bracket using two-color molding. One ofordinary skill in the art will also know how to incorporate typicaltwo-color molding processes known in the art for manufacturing articlesof manufacture that incorporate two or more different types of plasticmaterials. Orthodontic brackets depicted as including a plurality ofdifferent types of plastic materials are illustrated in FIGS. 21–23.

8. Two or More Initially Open Arch Wire Slots that Can be Ligated bySingle Cover.

An eighth improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooththat includes two or more different arch wire slots and a ligation coverthat is able to ligate two or more different arch wires in a singleaction of closing or locking the ligation cover relative to the base.Examples of brackets that include at least two initially open slots thatare ligated by the single action of locking or attaching a ligationcover to a bracket base are illustrated in FIGS. 5, 7, 8, 10, 12–20 and25.

The bracket base and ligation cover may comprise any appropriatematerial, such as metal, plastic or ceramic; They may be formed as anintegral, one-piece unit, or they may be separately formed and thenjoined together, such as by mechanical means, adhesion, or being fusedtogether (e.g., two-color molding of two separately molded plasticparts). If the ligation cover is made separately from the bracket base,it is either attached at one end to the base or it is attached over thebase by bringing the cover toward the base. The ligation cover ispreferably not slidably attached to the bracket base in this embodiment.

9. Bracket with Safety Locking Feature to Provide Enhanced Locking ofthe Ligation Cover to the Bracket Base.

A ninth improvement in the art is a self-ligating orthodontic bracketthat, at a minimum, includes a bracket base for attachment to a tooth, aligation cover that is able to absorb mechanical energy from an archwire, and a special locking feature that locks the cover to the basewith increasing force as more force is applied from an arch wire againstthe cover. In this way, the special locking feature prevents an archwire bearing outwardly against the ligation cover from undesirablyopening or unlocking the cover relative to the bracket base. Thisprovides a safety feature that prevents or inhibits orthodontic bracketsattached to particularly crooked teeth from inadvertently or prematurelyreleasing or relaxing its grip on the arch wire, which would typicallyrequire readjustment or replacement of the bracket by the orthodontist.Examples of orthodontic brackets that include a locking feature thatprovides this desired function are illustrated in FIGS. 13–20 and 25.

The bracket base and ligation cover may comprise any appropriatematerial, such as metal, plastic or ceramic. They may be formed as anintegral, one-piece bracket, or they may be separately formed and thenjoined together, such as by mechanical means, adhesion, or being fusedtogether (e.g., two-color molding of two separately molded plasticparts). The ligation cover may be hinged at one end and include thelocking feature at the free end, or the cover may be completelyremovable from the bracket base and include the locking features at bothends.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. An orthodontic bracket comprising: a bracket base having an uppersurface and an arch wire slot formed in the upper surface adapted toreceive at least one arch wire; and a ligation cover having anattachment portion for attachment of the ligation cover to the base, ahinged portion, and a hinge element interposed between and hingedlyinterconnecting the attachment portion and the hinged portion so as topermit hinged movement of the hinged portion relative to the attachmentportion, wherein the hinge element is a film hinge comprised of a localregion of reduced cross sectional thickness, wherein the hinged portionof the cover is movable about the hinge element over a substantial angleof rotation between a fully open, non-ligating position relative to thebracket base in which no portion of the ligation cover remains directlyover the arch wire slot and a closed, ligating position in which aportion of the ligation cover is directly over the arch wire slot, andwherein the ligation cover covers substantially all of the upper surfaceof the bracket base and the arch wire slot when the ligation cover is inthe closed, ligating position.
 2. An orthodontic bracket comprising: abracket base having a lower surface, a body portion and an uppersurface, the lower surface being adapted to be bonded to a tooth and theupper surface having an arch wire slot formed therein adapted to receiveat least one arch wire; a joint element having a first end connected tothe bracket base; and a ligation cover hingedly attached to a second endof the joint element opposite the first end by a hinge element so as topermit hinged movement of the ligation cover relative to the jointelement, wherein the hinge element is a film hinge comprised of a localregion of reduced cross sectional thickness, wherein the ligation thecover is movable about the hinge element between an open, non-ligatingposition relative to the bracket base in which no portion of theligation cover remains directly over the arch wire slot and a closed,ligating position in which a portion of the cover is directly over thearch wire slot, and wherein the ligation cover encloses substantiallyall of the body portion and the upper surface of the bracket base whenthe ligation cover is in the closed, ligating position.
 3. Anorthodontic bracket as defined in claim 2, the ligation cover coveringsubstantially all of the upper surface and the arch wire slot of thebracket base when the ligation cover is in the closed, ligatingposition.
 4. An orthodontic bracket as defined in claim 1 or 2, whereinthe attachment portion of the ligation cover or joint element isattached to the bracket base by inserting part of the attachment portionor joint element into a recess formed in the bracket base.
 5. Anorthodontic bracket as defined in claim 1 or 2, further comprising alatch mechanism for selectively locking the ligation cover to thebracket base in the closed, ligating position.
 6. An orthodontic bracketas defined in claim 1 or 2, further comprising opening means for urgingthe ligation cover to remain in the open, non-ligating position when inthe open, non-ligating position.
 7. An orthodontic bracket as defined inclaim 6, the opening means comprising a spring.
 8. An orthodonticbracket as defined in claim 6, the opening means comprising anelastomeric material having memory.
 9. An orthodontic bracket as definedin claim 1 or 2, further comprising closing means for urging theligation cover to remain in the closed, non-ligating position when inthe closed, non-ligating position.
 10. An orthodontic bracket as definedin claim 9, the closing means comprising a spring.
 11. An orthodonticbracket as defined in claim 9, the closing means comprising anelastomeric material having memory.
 12. An orthodontic bracket asdefined in claim 1, the bracket base comprising a plurality of archwireslots, at least two of which are substantially occluded by the ligationcover when in the closed, ligating position.
 13. An orthodontic bracketas defined in claim 1 or 2, the bracket base comprising plastic.
 14. Anorthodontic bracket as defined in claim 1 or 2, wherein the bracket basecomprises metal.
 15. An orthodontic bracket comprising: a metal bracketbase having an upper surface and an arch wire slot formed in the uppersurface adapted to receive at least one arch wire; and a plasticligation cover having an attachment portion for attachment of theligation cover to the base, a hinged portion, and a hinge elementinterposed between and hingedly interconnecting the attachment portionand the hinged portion so as to permit hinged movement of the hingedportion relative to the attachment portion, wherein the hinge element isa film hinge comprised of a local region of reduced cross sectionalthickness, wherein the hinged portion of the cover is movable about thehinge element over a substantial angle of rotation between a fully open,non-ligating position relative to the bracket base in which no portionof the ligation cover remains directly over the arch wire slot and aclosed, ligating position in which a portion of the ligation cover isdirectly over the arch wire slot, and wherein the ligation cover coverssubstantially all of the upper surface of the bracket base and the archwire slot when the ligation cover is in the closed, ligating position.16. An orthodontic bracket as defined in claim 15, wherein theattachment portion of the ligation cover is slidably attached to thebracket base.
 17. An orthodontic bracket as defined in claim 15, whereinthe attachment portion of the ligation cover is fixedly attached to thebracket base.